Women with breast cancer who develop brain metastases have a dismal prognosis and very few achieve long- term survival. Clinical outcomes for these patients have not significantly improved over the last several decades for a number of reasons including the poor penetration of most anticancer drugs across the blood- brain barrier, the specific exclusion of patients with brain metastases from the vast majority of clinical trials of experimental therapeutic agents, and an incomplete understanding of the biochemical and molecular events that are involved in the metastasis of primary breast tumors to the brain. Autophagy is an evolutionarily conserved lysosomal system of protein degradation that is utilized for the turnover of long-lived proteins and organelles. A number of recent studies have shown that autophagy plays an important role in cancer pathogenesis as it can function to provide a source of metabolic fuel to maintain cell survival under stressful conditions including those triggered by hypoxia and anticancer therapy. We and others have shown that autophagy significantly contributes to drug resistance and accordingly, that inhibiting this degradation pathway significantly augments the efficacy of multiple classes of cancer therapeutics and interferes with disease progression. However, the mechanistic basis for this has not been fully elucidated and the specific role that autophagy plays in the regulation of breast cancer metastasis nor its significance as a target for the prevention and therapy of metastatic disease has not been rigorously investigated. Our preliminary data indicate that a functional autophagy pathway may be required for primary breast tumors to metastasize to the brain, suggesting that targeting autophagy may be an effective approach to prevent and treat metastatic brain tumors. We recently discovered a novel inhibitor of autophagy that readily crosses the blood-brain barrier, has significant anti-neoplastic activity, and is therefore a very promising new candidate drug for the treatment of both primary and metastatic breast tumors. We hypothesize that genetic or pharmacological inhibition of autophagy will antagonize breast cancer progression, disrupt the establishment of metastatic tumors in the brain, and significantly augment the efficacy of the small molecule EGFR/HER2 inhibitor lapatinib. In Aim 1, we will investigate the specific roles that autophagy plays in the development and progression of primary and metastatic breast tumors. In Aim 2, we will determine the mechanism(s) by which autophagy inhibition enhances the anti-brain metastatic activity of lapatinib for the treatment of breast cancer. At the conclusion of these studies, we will have significantly expanded our knowledge regarding the role of autophagy in breast cancer pathogenesis and will have generated critical new information required to develop novel strategies to optimally target brain metastases for the treatment of breast cancer and other malignancies.